We have demonstrated the feasibility of a new imaging method, called Acoustic Radiation Force Impulse (ARFI) imaging in defining the mechanical properties of vascular tissue using ultrasonic radiation force. Results from the previous period of funding indicate that the method is capable of reliably distinguishing stiffness in cryogel models of human vascular tissues, including models of atherosclerotic plaques. In addition, we have demonstrated the ability of this technique to image the mechanical composition of in vivo carotid plaques in studies of the carotid artery in human volunteers and in excised animal and human arteries. We propose to further develop this technique for imaging moderate to highly stenotic plaques in the carotid artery, including the development of a 3-D imaging system to completely characterize the plaque and normal vasculature. We propose in vivo studies to develop and evaluate this technique in moderate to highly stenotic patients who are scheduled for endarterectomy and to correlate the resulting images with the histology of the excised samples. In addition, we propose an in vivo clinical study to assess the ability of combined 3-D ARFI/Doppler/B-mode images to predict the progression of the plaque and the necessity of surgical treatment for asymptomatic patients based on the morphology and mechanical composition of the carotid plaque. PUBLIC HEALTH RELEVANCE: We have developed a new imaging method that displays the stiffness of blood vessels and of the plaques that can clog vessels. We propose to improve this method and to install it on a clinical ultrasonic scanner. We will then test whether it can, by classifying plaques in the carotid artery as either soft or hard, predict which patients will have strokes over a two year period.